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Abstract

Enediyne compounds have captured the imagination of chemists since their
discovery as a class of natural products. Because of their cytotoxicity, these compounds
are not suitable for use in cancer treatment. As a result, chemists have aimed to reduce
their toxicity, improve stability and elucidate the mechanism of their cyclization reaction.
The Sonogashira coupling reaction is used to synthesize a number of heteroaromatic
enediynes and has been examined. By coupling a number of alkynes with 2,3-
dibromothiphene a number of corresponding disubstituted enediynes were produced. In
order to get fused bicyclic heteroaromatic products both thermal and photochemical
Bergman cyclizations have been performed with these enediynes. To date, the attempted
cyclizations have not been successful.
Beside this, a series of competitive reactions was carried out to determine the
relative reactivity of substituted aryl iodides in the Sonogashira reactions. These reactions
were carried out in co-catalyst system composed of Pd/Cul. The competitive reactions
between iodobenzene and a number of 3- and 4-substituted iodobenzenes provided
relative rates which were compared to the theoretical electron densities of the iodidebearing
carbon. Generally, electron withdrawing substituents in the para- and metapositions
increased the reactivity, while donating substituents decreased the rate of
reaction. It was found that resonance effects have a greater effect on reactivity than
inductive effects.